High Space-time Yield Research Articles

Hydrogenolysis of cellulose to valuable chemicals over activated carbon supported mono- and bimetallic nickel/tungsten catalysts

The hydrogenolysis of cellulose was systematically investigated at 488 K and under 65 bar H2 in the absence of a catalyst and over six different catalytic systems containing nickel and/or tungsten on activated carbon (AC) in order to understand the role of individual active components (AC, W/AC, Ni/AC, a physical mixture of Ni/AC + W/AC, and two differently prepared Ni/W/AC catalysts) with respect to the product distribution wherein polyols (e.g. ethylene glycol (EG), propylene glycol, and sorbitol) are highly valuable chemicals. Without a catalyst and when using only AC, a hydrochar, due to hydrothermal carbonization of cellulose, was obtained. Although the catalyst W/AC was effective for the degradation of cellulose (high conversion of 90%) and facilitates C–C bond cleavage, selective production of any product was not possible, and the carbon efficiency (CEL) is the lowest (9.1%). Also, with highly dispersed Ni on AC the polyol yield was only 5.3%. The desired behavior showed Ni/W/AC provided its preparation occurs by a two-step incipient wetness (IW) technique. Starting with a remarkably high cellulose/catalyst ratio of 10, a cellulose conversion of 88.4%, CEL of 78.4% and EG yield of 43.7% were achieved (overall polyol yield = 62.1%). Drastically lower yields towards EG by an order of magnitude and decreased CEL were obtained by a co-impregnated Ni/W/AC catalyst and the Ni/AC + W/AC mixture. By the detailed analysis via XRD, TPR and CO chemisorption, it can be concluded that in the Ni/W/AC catalyst, after the first IW step of the activated carbon with ammonium metatungstate hydrate and the following reduction in H2 up to 1128 K, metallic tungsten was formed. This leads, in combination with the hydrogenation properties of nickel introduced in the second IW step, to a virgin bimetallic catalyst, i.e. before the hydrogenolysis starts, in which both components must be metallic. This is a prerequisite for high polyol production. Finally, varying the AC type, high space–time-yields up to 2.5 g polyols (gcatalyst h)−1 were obtained. A slight deactivation after two runs followed by a strong decrease of polyol yield in the next two runs was observed. Leaching and structural changes on the catalyst surface (formation of NiWO4) are mainly responsible for deactivation.

Mass and heat transfer enhancement at the wall of cylindrical agitated vessel by turbulence promoters

Rates of liquid–solid mass transfer at a wall of stirred tank reactor lined with an array of vertical tubes turbulence promoter were studied using the dissolution of copper in acidified dichromate technique. Parameters studied are physical properties of the solution, impeller geometry, impeller rotation speed, cylinder diameter, circumferential distance between the vertical cylinders, and the effect of drag reducing polymers. The presence of vertical cylinders at the reactor wall increased the volumetric mass transfer coefficient compared to the presence of the wall without the cylinders by an amount ranging from 12.5% to 214.5%. The presence of Polyox WSR-301 drag reducing polymer decreased the rate of mass transfer by an amount ranging from 3.5% to 32.26% depending on polymer concentration and impeller rotation speed. All data were correlated by dimensionless mass transfer equations. The importance of the present results in building high space time yield catalytic reactors suitable for conducting diffusion controlled reactions was highlighted, also the possible role of the vertical tube array as a secondary built in heat transfer facility which assists external cooling jacket was noted.

In Situ Energy-Dispersive X-ray Diffraction for the Synthesis Optimization and Scale-up of the Porous Zirconium Terephthalate UiO-66

The synthesis optimization and scale-up of the benchmarked microporous zirconium terephthalate UiO-66(Zr) were investigated by evaluating the impact of several parameters (zirconium precursors, acidic conditions, addition of water, and temperature) over the kinetics of crystallization by time-resolved in situ energy-dispersive X-ray diffraction. Both the addition of hydrochloric acid and water were found to speed up the reaction. The use of the less acidic ZrOCl2·8H2O as the precursor seemed to be a suitable alternative to ZrCl4·xH2O, avoiding possible reproducibility issues as a consequence of the high hygroscopic character of ZrCl4. ZrOCl2·8H2O allowed the formation of smaller good quality UiO-66(Zr) submicronic particles, paving the way for their use within the nanotechnology domain, in addition to higher reaction yields, which makes this synthesis route suitable for the preparation of UiO-66(Zr) at a larger scale. In a final step, UiO-66(Zr) was prepared using conventional reflux conditions at the 0.5 kg scale, leading to a rather high space-time yield of 490 kg m(-3) day(-1), while keeping physicochemical properties similar to those obtained from smaller scale solvothermally prepared batches.

Mass and heat transfer behavior of a rough vertical vibrating cylinder in relation to annular electrochemical and catalytic reactor design

Rates of mass transfer were measured at a vibrating rough (V threaded) vertical cylinder by the electrochemical technique. Variables studied were frequency and amplitude of oscillation, and degree of surface roughness. The rate of mass transfer at the rough vibrating cylinder was found to increase by a factor ranging from 2.75 to 6.1 compared to the smooth vibrating cylinder depending on the operating conditions. In general the enhancement ratio increases with increasing ReV especially at high amplitudes; for low amplitudes it passes through a maximum and then decreases with further increase in ReV. The data for oscillating rough cylinder were correlated by the equation:ShL=0.535Sc0.33ReV,L0.5eP0.67A mathematical model based on the surface renewal theory was found to correlate the present data with a standard deviation of 7.29%. Implications of the present study for the design and operation of high space time yield annular catalytic and electrochemical reactors used to conduct diffusion controlled reactions was noted. Also the importance of the present results to the design and operation of annular dialyzers using corrugated vibrating cylindrical membrane was highlighted.

Ammoxidation of 2-methylpyrazine to 2-cyanopyrazine over Nb–V oxides: marked effect of the Nb/V ratio on the catalytic performance

Among various Nb–V–O catalysts, the catalyst with a Nb/V ratio of 1 has shown the best activity and selectivity as well as extremely high space–time yields (X-MP ~100%, S-CP ~70% and STY = 440 gCP kgcat−1 h−1).

A water-based and high space-time yield synthetic route to MOF Ni2(dhtp) and its linker 2,5-dihydroxyterephthalic acid

Highway to MOF Ni2(dhtp)! 1 hour in boiling water under atmospheric pressure; a cheap synthesis of the linker is also reported.

From 'Lab & Light on a Chip' to Parallel Microflow Photochemistry

Continuous-flow microreactors offer major advantages for photochemical applications. This mini-review summarizes the technological development of microflow devices in the Applied and Green Photochemistry Group at James Cook University, and its associates, from fixed microchips for microscale synthesis to flexible multicapillary systems for parallel photochemistry. Whereas the enclosed microchip offered high space–time-yields, the open capillary-type reactor showed a greater potential for further modifications. Consequently, a 10-microcapillary reactor was constructed and used successfully for process optimization, reproducibility studies, scale-up, and library synthesis. To demonstrate the superiority of microflow photochemistry over conventional batch processes, the reactors were systematically evaluated using alcohol additions to furanones as model reactions. In all cases, the microreactor systems furnished faster conversions, improved product qualities, and higher yields. UVC-induced [2+2] cycloadditions of furanone with alkenes were exemplarily examined in a capillary reactor, thus proving the broad applicability of this reactor type.

Highly Efficient Synthesis of (R)-3-Quinuclidinol in a Space–Time Yield of 916 g L–1 d–1 Using a New Bacterial Reductase ArQR

A new keto reductase (ArQR), identified from Agrobacterium radiobacter ECU2556, can efficiently reduce 3-quinuclidinone in excellent enantioselectivity and high space-time yield for the synthesis of (R)-3-quinuclidinol, a chiral building block of many antimuscarinic agents. This is the first time that a high yield of (R)-3-quinuclidinol up to 916 g L(-1) d(-1) using a bioreduction approach is reported.

Characterization of a newly synthesized carbonyl reductase and construction of a biocatalytic process for the synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate with high space-time yield

A carbonyl reductase (SCR2) gene was synthesized and expressed in Escherichia coli after codon optimization to investigate its biochemical properties and application in biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), which is an important chiral synthon for the side chain of cholesterol-lowering drug. The recombinant SCR2 was purified and characterized using ethyl 4-chloro-3-oxobutanoate (COBE) as substrate. The specific activity of purified enzyme was 11.9 U mg(-1). The optimum temperature and pH for enzyme activity were 45 °C and pH 6.0, respectively. The half-lives of recombinant SCR2 were 16.5, 7.7, 2.2, 0.41, and 0.05 h at 30 °C, 35 °C, 40 °C, 45 °C, and 50 °C, respectively, and it was highly stable in acidic environment. This SCR2 displayed a relatively narrow substrate specificity. The apparent K m and V max values of purified enzyme for COBE are 6.4 mM and 63.3 μmol min(-1) mg(-1), respectively. The biocatalytic process for the synthesis of (S)-CHBE was constructed by this SCR2 in an aqueous-organic solvent system with a substrate fed-batch strategy. At the final COBE concentration of 1 M, (S)-CHBE with yield of 95.3% and e.e. of 99% was obtained after 6-h reaction. In this process, the space-time yield per gram of biomass (dry cell weight, DCW) and turnover number of NADP(+) to (S)-CHBE were 26.5 mmol L(-1) h(-1) g(-1) DCW and 40,000 mol/mol, respectively, which were the highest values as compared with other works.

Fischer–Tropsch synthesis over precipitated iron catalysts supported on carbon

Fischer–Tropsch synthesis was conducted over carbon-supported iron catalysts at 260–280°C and 2.0MPa. Potassium addition enhances the selectivity to liquid hydrocarbons greatly. A high space time yield of total hydrocarbons of 450gkg−1h−1 was attained over K-promoted active carbon-supported catalyst. Ozone treatment of the active carbon surface is found to be effective for the catalyst durability. It is inferred that enlarged average pore diameter plays an important role for the stability by the smooth extraction of the waxy products.

A versatile, industrially relevant, aqueous room temperature synthesis of HKUST-1 with high space-time yield

A facile aqueous room temperature synthesis method has been developed to synthesize HKUST-1 from nano-materials to micro- and hierarchical porous structures by tuning either the copper source or the reaction time. The synthesis is readily scalable, with space-time yield >2000 kg m−3 day−1.

Chemicals from agricultural biomass: chemoenzymatic approach for production of vinylphenols and polyvinylphenols from phenolic acids

A two-step chemoenzymatic process for the preparation of polyvinylphenols from phenolic acids (PAs), being abundant aromatic constituents found in agricultural biomass, was developed. In the first step, conversion of 4-hydroxycinnamic acid derivatives to the corresponding vinylphenols, mediated by a recombinant phenolic acid decarboxylase, was evaluated using a variety of bioprocessing technologies that include biphasic whole cell and cell free extract biotransformations, a combination of biocatalyst with adsorbent resins for in situ product recovery, and fixed bed reactors using immobilized whole cells. The best yield (90%) with a high space time yield of 4.83 g/l/h was the result of a combination of crude enzyme extracts of the recombinant Escherichia coli (E. coli) with water immiscible organic solvents such as toluene. In the second step, cationic and radical polymerizations were tested to produce polyvinylguaiacol (PVG) from vinyl phenols. Characterization of PVG by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and nanoindentation test are reported here for the first time. The feasibility of the chemoenzymatic process for the production of aromatic polymers from biomass was demonstrated by the production of polymers from a mixture of ferulic acid (FA) and p-coumaric acid (pCA), obtained from alkaline hydrolysis of corn bran. Interestingly, nanoindentation tests showed that both PVG and “mixed” PVG polymers showed significantly higher performances than a commercial polystyrene polymer.

Green scalable aerosol synthesis of porous metal–organic frameworks

Benchmarked micro or nanosized HKUST-1, ZIF-8 and Fe3(BTC)2 as well as template-assisted Fe3(BTC)2 metal-organic frameworks (MOFs) of various morphologies were synthesized via a green and scalable aerosol route. Their high space time yields make this continuous method very promising for the industrial production and shaping of MOFs.

Scalable Room‐Temperature Conversion of Copper(II) Hydroxide into HKUST‐1 (Cu3(btc)2)

Copper(II) hydroxide is converted directly to HKUST-1 (Cu(3) (btc)(2) ) after only 5 min at room-temperature in aqueous ethanolic solution without the need of additional solvents. Scale up to the kilogram scale does not influence porous properties yielding pure-phase product with a remarkable total surface area exceeding 1700 m(2) g(-1) featuring aggregates of nanometer-sized crystals (<600 nm) and extremely high space-time yields.

Cu/SiO2 hybrid catalysts containing HZSM-5 with enhanced activity and stability for selective hydrogenation of dimethyl oxalate to ethylene glycol

A novel type of hybrid catalysts composed of Cu/SiO2 and H-form ZSM-5 (HZSM-5) zeolite, prepared using urea-assisted gelation method, displayed excellent catalytic activity and stability for the selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The content and SiO2/Al2O3 ratio of HZSM-5 significantly influenced the performance of hybrid catalysts. An unprecedentedly high EG space time yield of 1.50gg-cat−1h−1, with DMO conversion of 99.5% and EG selectivity of 94.8%, were obtained on a hybrid catalyst containing 3wt% of HZSM-5 with SiO2/Al2O3=38. The characterizations of N2 physisorption and N2O chemisorptions revealed that both specific surface area and copper dispersion were promoted by introducing HZSM-5 zeolite into the Cu/SiO2 catalyst. Moreover, X-ray Auger electron spectroscopy and in situ Fourier transform infrared spectroscopy of chemisorbed CO demonstrated that the surface Cu+ site concentration of the catalysts containing HZSM-5 was higher than those without HZSM-5. The results indicated that the introduction of HZSM-5 zeolite changed the crystallization behaviors of cupric phyllosilicate precursor, essentially improving copper dispersion and enhancing copper–silica interaction. Furthermore, the specific zeolitic cages and negatively charged framework of HZSM-5 zeolite incorporated into Cu/SiO2 entities might also be beneficial for accommodation and stabilization of highly dispersed cuprous species, which act as efficient active sites for the activation of ester groups.

Mass Transfer at a Vertical Oscillating Screen Stack in Relation to Catalytic and Electrochemical Reactor Design

The aim of the present work is to improve the performance of the parallel plate catalytic and electrochemical reactor in conducting diffusion controlled reactions by using parallel oscillating vertical arrays of closely packed screens. To this end, rates of mass transfer at oscillating vertical single screen and arrays of closely packed screens were studied by measuring the limiting current of the cathodic deposition of copper from acidified copper sulfate. Variables studied were amplitude and frequency of vibration, screen mesh number, and number of screens per stack. The mass transfer data at a single vibrating screen were correlated by the equation: Sh = 0.73Sc0.33Rev0.38. Increasing mesh number of the screen was found to increase the mass transfer coefficient, while increasing the number of screens per stack decreased the mass transfer coefficient below single screen value. The enhancement ratio between oscillating screen array and oscillating vertical plate (the volumetric mass transfer coefficient ratio) ranged from 11.7 to 27.87 depending on the operating conditions. Electrical energy consumption of the present reactor was found to be lower than the value reported in the literature for electrowinning of copper using traditional parallel plate reactor. In view of this, the possibility of using oscillating vertical screen stack in building high space-time yield modular parallel plate electrochemical reactor suitable for wastewater treatment, electroorganic synthesis, and electrochemical energy storage via redox cells was noted. Also, the possibility of using the present geometry in building catalytic reactors suitable for conducting diffusion controlled liquid–solid reaction was highlighted.

Continuous D‐Fructose Dehydration to 5‐ Hydroxymethylfurfural Under Mild Conditions

The dehydration of D-fructose to 5-hydroxymethylfurfural was studied under single-phase conditions in the low boiling solvent 1,4-dioxane at moderate temperatures in the presence of the solid acid-catalyst Amberlyst-15. The reaction was first examined and optimized under batch conditions, where it was found that the yield could be increased up to 75 % by adding small amounts of DMSO. Subsequently, the reaction was performed under continuous flow in a fixed bed reactor. Internal and external mass transfer limitations could be eliminated by changing the particle size and by adjusting the flow rate. Under continuous conditions, the HMF yield could be further increased to 92 %; the space-time yield was found to be 75 times higher compared to the batch case. A long-term stability test (96 h), including solvent regeneration, demonstrated that the catalyst is stable over time. Additionally, it was shown that even small amounts of water have a negative effect on the HMF yield. Overall, the present system shows a good alternative to other systems presented in literature because high space-time yields and selectivities were obtained under relatively mild and continuous conditions.

Efficient Synthesis of a Chiral Precursor for Angiotensin-Converting Enzyme (ACE) Inhibitors in High Space-Time Yield by a New Reductase without External Cofactors

A new reductase, CgKR2, with the ability to reduce ethyl 2-oxo-4-phenylbutyrate (OPBE) to ethyl (R)-2-hydroxy-4-phenylbutyrate ((R)-HPBE), an important chiral precursor for angiotensin-converting enzyme (ACE) inhibitors, was discovered. For the first time, (R)-HPBE with >99% ee was produced via bioreduction of OPBE at 1 M without external addition of cofactors. The space-time yield (700 g·L(-1)·d(-1)) was 27 times higher than the highest record.

Large scale fluorine-free synthesis of hierarchically porous iron(III) trimesate MIL-100(Fe) with a zeolite MTN topology

The hierarchically mesoporous iron(III) trimesate MIL-100(Fe) with a zeolite-MTN topology is known as an advanced functional material that is biocompatible. In this work, the large scale synthesis of MIL-100(Fe) has been achieved by hydrothermal reactions using suitable conditions without HF for the large scale synthesis. Although such conditions are narrow, the concurrent change of iron precursor and increase in the concentration of reaction mixture give rise to a synergetic effect leading to an increase in the crystallinity of F-free MIL-100(Fe). This method, combined with two purification steps (solvent extraction and chemical treatment with NH4F) leads to a highly porous F-free material obtained throughout a very high space–time-yield (>1700kg/m3day). Possible formation mechanisms of MIL-100(Fe) under hydrothermal conditions have been proposed in terms of four steps such as hydrolysis, deprotonation, self-assembly, and polycondensation. The resulting material exhibits similar physicochemical properties to those of the one prepared in the presence of HF, except for a slight difference in sorption capacities of gases and liquid vapors corresponding to the difference of pore volume. Regardless of the use of HF, the purified MIL-100(Fe) possesses very high uptakes for both non-polar toluene and polar ethanol probe molecules due to the respective interactions with hydrophilic and hydrophobic sites in the framework. Finally, hydrophobicity measurements confirm that the dehydrated MIL-100(Fe) is more hydrophobic than conventional zeolite beta (SiO2/Al2O3=25) and commercial iron trimesate (Basolite F300) from BASF SE.

High Throughput Development of Selective Oxidation Catalysts at Sud-Chemie

The Temkin reactor concept was successfully extended to the high throughput operation mode and it could be considerably improved as compared to the original design with respect to an optimized gas flow pattern over the full size beads. This improved parallel reactor design was successfully used for the high throughput optimization of an innovative new class of physically coated VAM shell catalysts. Exploiting this novel, improved Temkin reactor concept allowed Süd-Chemie not only to optimize the multiparameter compositional space of noble metal and promoter loadings on the support spheres but for the first time to combine this "chemical optimization" with the high throughput improvement of catalytically decisive parameters as the active shell thickness, the metal distribution cross the shell, the pore diameters, and the pore volumes. This new class of physically impregnated VA catalysts, called VAM²ax, impress by its exceptionally high VA selectivity of above 94% at 50% oxygen conversion and the very high space time yields of > 1000 g VAM/l*h which easily can be reached over these shell catalysts with optimized mass and heat transport properties.